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I’ve posted a small number of excellent pyrite iron cross twins from Colombia in this update (click here).

“Iron-cross twins” are twinned crystals exhibiting the forms of two pentagonal dodecahedra (also known as pyritohedra). These twins display edges crossing at 90 degrees, and in an idealized/model twin, these edges form a cross. In nature, the edges that form the cross are sometimes not continuous or are not equal to one another, so a pyrite crystal that is twinned according to the iron-cross law may or may not exhibit an actual cross shape, but in any event the relationship of the crystals exhibits the “crossed” symmetry.

The iron cross twin law is well known and exhibited in specimens from various localities, but rarely does one find good-sized complete crystals. These remarkable specimens are from a find about a year ago near Gachalá, Colombia. They are superb iron-cross twins.

These were being sold as “limonite” pseudomorphs after pyrite, but they are not. They are pyrite crystals with a thin surface veneer of goethite.

I’ve added excellent specimens from two great Peruvian localities in this Peru Update (click here) – tennantite specimens from Mundo Nuevo and pyrite specimens from Huanzala.

The Mundo Nuevo tennantites are excellent specimens for the species. Mined during 2014-15 specimen recovery work, they are part of a find that has now been analyzed quite extensively. Of those (over 40 specimens tested) all were tennantite except one that was a borderline tennantite-tetrahedrite. Accordingly, specimens from this find are now labelled tennantite. I have not had each of these analyzed, given the pervasive tennantite results (and not wanting to add to their prices by incurring unnecessary cost). These tennantites were originally posted on this website labelled “tetrahedrite”, as they were sold to me under that label – they were then removed from the site until the analysis work on the find had been completed.